Method of making a transparency of a colored image in a magneto-electric printing system

ABSTRACT

A transparency of a colored image is produced on a lighttransmitting recording element, comprising a photoconductive layer and a tricolor mosaic filter layer, by a single-exposure method wherein (a) the photoconductive layer is uniformly charged electrostatically and uniformly covered with magneto-electric particles; (b) a magnetic field of a strength just insufficient to remove the particles from the photoconductive layer is applied adjacent to the particles; and (c) the photoconductive layer is exposed through the tricolor mosaic filter, while in the magnetic field, with a light image of the colored image to be produced.

United States Patent [191 Giaimo, Jr.

[ Aug. 5, 1975 METHOD OF MAKING A TRANSPARENCY OF A COLORED IMAGE IN A MAGNETO-ELECTRIC PRINTING SYSTEM [75] Inventor: Edward Charles Giaimo, Jr.,

Princeton, NJ.

[58] Field of Search 96/1 R, 1.4, 1.2; ll7/17.5

[56] References Cited UNITED STATES PATENTS 7/1957 Moncrieff-Yeates 96/1 R X 2/ l 960 Bertelsen 1/1961 Gundlach 96/1 R 3,093,039 6/1963 Rheinfrank 96/l.4 X 3,392,642 7/1968 Germer 3,413,117 11/1968 Gaynor 96/l.2 3,707,138 12/1972 Cartwright ll7/l7.5 X

Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or FirmH. Christoffersen; R. P. Williams; A. I. Spechler 5 7 ABSTRACT A transparency of a colored image is produced on a light-transmitting recording element, comprising a photoconductive layer and a tricolor mosaic filter layer, by a single-exposure method wherein (a) the photoconductive layer is uniformly charged electrostatically and uniformly covered with magneto-electric particles; (b) a magnetic field of a strength just insufficient to remove the particles from the photoconductive layer is applied adjacent to the particles; and (c) the photoconductive layer is exposed through the tricolor mosaic filter, while in the magnetic field, with a light image of the colored image to be produced.

1 Claim, 6 Drawing Figures PATENTEUAUG 5I9I5 3,898,082 SHEET 2 I I l WFELEWHITE LIGHT IiUEI RED IBLACK IGREENIWHITE I""38 BLUE RED NO GREEN WHITE LIGHT LIGHT LIGHT LIGHT HT I2 I4 4 [O GBRGBRGBRGBRGB 22 UNIFORM WHITE W LIGHT I4 RGBRGBRGBRGBRGB l8 I I I I I I I I x I LU l IE IS 5% E; I 9- m {mu n :QI D: 3 I I I I l I I L J METHOD OF MAKING A TRANSPARENCY OF A COLORED IMAGE IN A MAGNETO-ELECTRIC PRINTING SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to the art of electrostatic printing in color, and, more particularly, to a method of making a transparency ofa colored image in a magneto-electric printing system. The novel method is particularly suitable for making transparencies of colored images, with a single exposure, on a lighttransmitting recording element that may be viewed immediately and erased easily, if so desired.

It has been proposed, in US. Pat. No. 3,458,309 issued to J. Gaynor, to provide color transparencies by an electrophotographic method wherein a lighttransmitting recording element, including a tricolor mosaic filter layer and a photoconductive layer, is elestrostatically charged; and the recording element is exposed to a colored light image to form a latent electro static image which is subsequently developed with electroseopic particles. While this prior-art method is satisfactory for many applications, the colored image produced cannot be monitored and its development controlled easily during the development thereof. Also, the developed colored image cannot be erased with the same apparatus used to develop the image with the particles.

It has also been proposed to use magnetic toner particles in an electrostatic printing system, and to effect a removal of the magnetic toner particles from a record ing element with the aid ofa magnetic field. While such a method is satisfactory for certain applications, it leaves something to be desired in others because the magnetic field does not always completely overcome the electrostatic field between the recording element and the magnetic toner particles; and some of the magnetic toner particles adhere tenaciously to the recording element, thereby preventing their complete removal.

In accordnace with the novel method, a transparency of a colored image on a light-transmitting recording element is produced with the aid of magneto-electric particles in a manner whereby the colored image may be visually monitored during its formation; and the image can be viewed, when formed, without removing the color transparency from a combined exposure, development and viewing station. Alternatively, the magneto-electric particles may be erased from the recording element, if so desired, with the same apparatus used for developing the recording element, and without the necessity of removing the recording element from the exposure, development, and viewing station.

SUMMARY OF THE INVENTION The novel method of making a transparency ofa colored image on a light-transmitting recording element. comprising a photoconductive layer and a tricolored mosaic filter layer, comprises the steps of: (a) charging the photoconductive layer uniformly, (b) covering the charged photoconductive layer uniformly with magneto-electric particles, (c) applying a magnetic field adjacent to the uniformly toned photoconductive layer, the magnetic field being of a strength just insufficient to remove the particles from the photoconductive layer, and (d) while in the magnetic field, exposing the uniformly covered photoconductive layer through the filter layer with a colored light image of the colored image to be produced on the color transparency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic illustration of a sideelevational view of a light-transmitting recording element used in the novel method;

FIG. 2 is a schematic view of one form of a tricolor mosaic filter layer viewed in the direction of lighttransmission; and

FIGS. 3, 4, 5, and 6 are schematic illustrations of the recording element, shown in FIG. 1, in sequential operations of being electrostatically charged, covered with magneto-electric particles, exposed, and viewed, respectively, in aecordance with the novel method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawings, there is shown a light-transmitting recording element 10 of the type used in the novel method. The recording element I0 comprises a light-transmitting substrate 12, a tricolored mosaic filter layer 14 on a major surface 16 of the substrate 12, a light-transmitting, electrically conductive layer 18 on a major surface 20 of the filter layer I4, and a photoconductive layer 22 on a major surface 24 of the conductive layer 18.

The light-transmitting substrate 12 may be rigid or flexible and may comprise a light-transmitting material, such as glass or a flexible plastic material, such as Mylar" or Cronar (E. I. DuPont De Nemours Co., Wilmington, Del), The electrically conductive layer 18 may comprise a Iighttransmitting, thin film of a metal, such as aluminum or chromium, for example, or a transparent layer of tin oxide and/or indium oxide.

The photoconductive layer 22 should be responsive to all of the colors in the visible spectrum and comprises a photoconductive layer of a light-transmitting material of the type described in US. Pat. No. 3,484,237, for Organic Photoconductive Compositions and Their Use in Electrophotographic Processes, or in the aforementioned US. Pat. No. 3,458,309, both patents being incorporated herein by reference. A light-transmitting recordingelement comprising a layer of dye-sensitized particulate zinc oxide in a resin binder may also be used.

The filter layer 14 may comprise a multiplicity of systematically, or randomly, arranged minute colored areas of a substantially equal number of each ofthree primary colors, designated as R, G, and B for the colors red, green, and blue, respectively. The elemental colored areas of the filter layer 14 illustrated in FIG. 2 are in a regular geometric pattern. A separate minute area of a primary color is provided for each elemental area of the image to be formed on a color transparency. Examples of the filter layer I4 and their method of manufacture are'described in the aformentioned US. Pat. No. 3,458,309 and US. Pat. No. 3,4l3,l l7, and are included herein by reference. Color filter layers, having a more or less statistically random distribution of irregularly shaped primary colored areas are described in the aformentioned patents. In any case, the maximum transverse dimension of each separate color R, G, or B area should be less than about 0.005 inch.

In the novel method, means are provided to electrostatically charge the photoconductive layer 22, in darkness, with a uniform electrostatic charge. To this end.

the conductive layer 18 of the recording element 10 is connected to a source of reference potential. such as ground. and a corona discharge device 26 of the type commonly used in the electrophotographic printing art, is disposed between the outer major surface 28 of the photoconductive layer 22 of the recording element 10. The corona discharge device 26 has a corona generating element 28, such as a thin wire. connected to the positive terminal of a high-voltage. unidirectional power supply 30. The negative terminal of the power supply is connected to ground. as is the shield 31 ofthe corona discharge device 26. The high voltage power supply 30 is capable of providing at least 5.000 volts. and the corona discharge device 26 is adapted to be moved over the recording element 10 in the directions of the double-headed arrow 32 to provide the photoconductive layer 22 with a uniform electrostatic charge. With the corona discharge device 26 connected as shown in FIG. 3, the surface 28 of the photoconductive layer 22 is charged positively, in darkness. It is also within the scope of the present invention to charge the surface 28 negatively.

The uniformly charged surface 28 of the photoconductive layer 22 is next covered, in darkness. uniformly with magneto-electric particles 34. as shown in FIG. 4. The magneto-electric particles 34 are attracted electrostatically to the electrostatically charged surface 28. The magneto-electric particles 34 comprise particles of magnetic material that may. or may not. be coated with a thermoplastic adhesive of any desired color. By the term magneto-electric particles as used herein. is meant particles of materials that are capable of being moved by both a magnetic field and an electric field. either separately or concurrently. The magnetoelectric particles 34 may comprise nickel, cobalt. or iron particles. for example. capable of being moved by a magnetic and/or an electric field. The average diameter of the magneto-electric particles 34 is not critical and may be between and 30 microns. The magnetoelectric particles 34 do not necessarily have to be spherical in shape. Suitable magneto-electric particles 34 for the novel method are described in US. Pat. Nos. 3,526.19l; 3,l06.479; and 3.093.039. for example. The magneto-electric particles 34 need not have an electroscopic charge thereon because electrostatically neutral magneto-electric toner particles 34 are attracted to a charged surface by what is believed to be electrostatic induction.

The magneto-electric particles 34 may be applied to the surface 28 by cascading them over the surface 28 from a container 36 held over an inclined recording element 10, as shown in FIG. 4. Other means of applying the magneto-electric particles 34 uniformly to the surface 28 may be employed. such as by passing the uniformly charged recording element l0 through a trough of magneto-electric particles 34.

Means are provided to expose. at an exposure station. the uniformly covered recording element with a single exposure of a colored light image of the image desired on the color transparency to be formed by the recording element 10. To this end. a colored light image as. for example. from a color transparency 38. such as a photographic Kodachromc" slide transparency. is projected (by directing white light onto the transparency 38) through the substrate 12, the color filter layer 14. and the conductive layer 18 onto the photoconductive layer 22, as shown in FIG. 5. The colored image on the tranparency 38 may comprise blue. red. black. green. and white portions. as indicated in FIG. 5. The projected blue. red. and green portions of the image of the transparency 38 will pass through blue. red. and green areas. respectively. of the tricolor mosaic filter layer 14 of the recording element 10. Any black portions of the transparency 38 will not pass through any of the colored areas of the filter layer 14'. and the projected white light of the transparency 38 will pass through each of the red. green. and blue areas upon which it impinges on the filter layer 14. The primary component colors of a color other than a primary color are transmitted through the appropriate primary colors of the filter layer 14.

A magnetic field of a strength just insufficient to remove the particles 34 from the surface 28 of the recording element 10, in the absence of any exposure of the recording element 10, is disposed adjacent the surface 28. Thus. an electromagnet 40 in the form of a toroid (illustrated in FIG. 5 in cross section) is disposed adjacent to the surface 28 to provide a substantially uniform magnetic field just insufficient to remove the magneto-electric particles 34 from the surface 28 in the absence of any exposure of the recording element 10. The electromagnet 40 is energized from a suitable source 42 of electrical energy. such as a battery. connected through a single-pole single-throw switch 44 and a rheostat 46. The proper strength of a desired magnetic field adjacent to the surface 28 of the photoconductor 22 is obtained by closing the switch 44 and adjusting the rheostat 46. When the photoconductive layer 22 is exposed by light from the colored image of the transparency 38, the electrostatic attraction between the magncto-electric particles 34 and the photoconductive layer 22 at the exposed portions is reduced; and the affected magneto-electric particles 34 are removed from the exposed areas of the photoconducti e layer 22 by the magnetic field. as shown in FIG. 5. The amount of magnetoelectric particles 34 that are removed by the exposure of any elemental area of the photoconductive layer 22 is proportional to the intensity of light of the exposure thereat.

The exposure and development (selective removal of some particles 34 from the surface 28) of the recording element 10, at the developing station. as shown in Flg. 5, may be monitored by an observer viewing the image being formed on the surface 28 by looking through the opening 48 in the toroid of the electromagnet 40 during the exposure process. When the image formed on the surfaces 28 of the recording element 10 appears to be fully developed. (by the formation of selective. lighttransparent areas on the surface 28). the exposure may be extinguished. as by turning off the white light that projects the colored image from the transparency 38 onto the recording element 10. and/or by opening the switch 44 and removing the magnetic field from adjacent the surface 28. The colored image being devel oped on the surface 28 may also be monitored by projccting the image as it is formed. during the exposure period. onto a screen (not shown) with a suitable optical system (not shown.

The developed recording element 10 is a transparency of the colored image projected onto it from the transparency 38'. and this colored image may be viewed. like any photographic transparency. by directing uniform white light through the developed record ing element 10. as shown in FIG. 6. The magnetoelectric particles 34 may be fixed to the surface 28 of the recording element by spraying a transparent adhesive onto the magneto-electric particles 34. if the magneto-electric particles 34 are coated with a thermoplastic material, they may be fixed to the surface 28 by heating them to meltthe thermoplastic coating so that vthe particles 34 may adhere to the surface 28.

moved from the surface 28, at the combined exposure,

developing and viewing station, as shown in FIG. 5, by increasing the strength of the magnetic field of the electromagnet 40, by adjusting the rheostat 46 so as to i send more current through the electromagnet 40. The

strength of the magnetic field may be increased so that all the magneto-electric particles 34 are pulled from the surface 28 without removing the recording element 10 from the exposure station. The removal of the magneto-electric-particles 34 may also be enhanced by exposing the recording element 10 with white light, preferably through the filter layer 14, so as to increase the photoconductivity of the photoconductive layer 22. This procedure reduces the electrostatic attraction between the magneto-electric particles 34 and the photoconductive layer 22 so that the particles 34 may be removed easily by the magnetic field.

I claim;

1. A method of making 'a transparency of a colored image on a light-transmitting recording element comprising a color-sensitive photoconductive layer and a tricolor mosaic filter layer, said filter layer comprising a multiplicity of systematically, or randomly, arranged minute colored areas ofa substantially equal number of each of three primary colors, and a separate minute area of a primary color being for each elemental area of said colored image, said method comprising the steps of:

charging said photoconductive layer uniformly with an electrostatic charge, covering said charged photoconductive layer uniformly with magnetic particles,

applying an adjustable magnetic field adjacent to said uniformly covered photoconductive layer, said magnetic field being adjusted to a strength just insufficient to remove said particles from said photoconductive layer, exposing said uniformly covered photoconductive layer, while in said magnetic field, with a colored light image of the image desired on the transpar' ency, to reduce the electrostatic attraction between the exposed portions of said photoconductive layer and certain magnetic particles thereat. and to remove said certain magnetic particles from said photoconductive layer by said magnetic field, whereby said colored image may be viewed by light transmitted through said recording element, said adjustable magnetic field being applied adjacent said uniformly covered photoconductive layer with an electromagnet in the form of a toroid having an unobstructed opening therein, and observing said photoconductive layer through said unobstructed opening in said toroid during the step of exposing said photoconductive layer, and removing said certain magnetic particles whereby to monitor the development of the image on said transparency. 

1. A METHOD OF MAKING A TRANSPRENCY OF A COLORED IMAGE ON A LIGHT-TRANSMITTING RECORDING ELEMENT COMPRISING A COLORSENSITIVE PHOTOCONDUCTIVE LAYER AND A TRICOLOR MOSAIC FILTER LAYER, SAID FILTER LAYER COMPRISING A MULTIPLICITY OF SYSTEMATICALLY, OR RANDOMLY, ARRANGED MINUTE COLORED AREAS OF A SUBSTANTIALLY EQUAL NUMBER OF EACH OF THREE PRIMARY COLORS, AND A SEPARATE MINUTE AREA OF A PRIMARY COLOR BEING FOR EACH ELEMENTAL AREA OF SAID COLORED IMAGE, SAID METHOD COMPRISING THE STEPS OF: CHARGING SAID PHOTOCONDUCTIVE LAYER UNIFORMLY WITH AN ELECTROSTATIC CHARGE, COVERING SAID CHARGED PHOTOCONDUCTIVE LAYER UNIFORMLY WITH MAGNETIC PARTICLES, APPLYING AN ADJUSTABLE MAGNETIC FIELD ADJACENT TO SAID UNIFORMLY COVERED PHOTOCONDUCTIVE LAYER, SAID MAGNETIC FIELD BEING ADJUSTED TO A STRENGTH JUST INSUFFICIENT TO REMOVE SAID PARTICLES FROM SAID PHOTOCONDUCTIVE LAYER, EXPOSING SAID UNIFORMLY COVERED PHOTOCONDUCTIVE LAYER, WHILE IN SAID MAGNETIC FIELD, WITH A COLORED LIGHT IMAGE OF THE IMAGE DESIRED ON THE TRANSPARENCY, TO REDUCE THE ELECTROSTATIC ATTRACTION BETWEEN THE EXPOSED PORTIONS OF SAID PHOTOCONDUCTIVE LAYER AND CERTAIN MAGNETIC PARTICLES THEREAT, AND TO REMOVE SAID CERTAIN MAGNETIC PARTICLES FROM SAID PHOTOCONDUCTIVE LAYER BY SAID MAGNETIC FIELD, WHEREBY SAID COLORED IMAGE MAY BE VIEWED BY LIGHT TRANSMITTED THROUGH SAID RECORDING ELEMENT, SAID ADJUSTABLE MAGNETIC FIELD BEING APPLIED ADJACENT SAID UNIFORMLY COVERED PHOTOCONDUCTIVE LAYER WITH AN ELECTROMAGNET IN THE FORM OF A TOROID HAVING AN UNOBSTRUCTED OPENING THEREIN, AND OBSERVING SAID PHOTOCONDUCTIVE LAYER THROUGH SAID UNOBSTRUCTED OPENING IN SAID TOROID DURING THE STEP OF EXPOSING SAID PHOTOCONDUCTIVE LAYER, AND REMOVING SAID CERTAIN MAGNETIC PARTICLES WHERE TO MONITOR THE DEVELOPMENT OF THE IMAGE ON SAID TRANSPARENCY. 